MHC Class I Polypeptide Related Sequence A (MICA) is a stress-induced cell surface protein. It belongs to the MHC class I-like molecules but has distinct features. MICA is highly expressed on cells under stress, such as those with DNA damage or infected cells. Structurally, it has a domain structure that allows for interactions with other molecules.MICA can function as a ligand and binds to Killer Cell Lectin Like Receptor Subfamily D, Member 1 (KLRD1, also known as NKG2D) on the surface of natural killer (NK) cells and some T cells. This binding activates immune cells and enables them to participate in the body's immune surveillance and defense responses.Thus a functional ELISA assay was conducted to detect the interaction of recombinant human MICA and recombinant human KLRD1. Briefly, MICA was diluted serially in PBS with 0.01% BSA (pH 7.4). Duplicate samples of 100 μl were then transferred to KLRD1-coated microtiter wells and incubated for 1h at 37℃. Wells were washed with PBST and incubated for 1h with anti-MICA pAb, then aspirated and washed 3 times. After incubation with HRP labelled secondary antibody for 1h at 37℃, wells were aspirated and washed 5 times. With the addition of substrate solution, wells were incubated 15-25 minutes at 37℃. Finally, add 50 μL stop solution to the wells and read at 450/630nm immediately. The binding activity of recombinant human MICA and recombinant human KLRD1 was shown in Figure 1, the EC50?for this effect is 0.582ug/mL.